Method and apparatus for sorting elements in hardware structures

ABSTRACT

A method for sorting elements in hardware structures is disclosed. The method comprises selecting a plurality of elements to order from an unordered input queue (UIQ) within a predetermined range in response to finding a match between at least one most significant bit of the predetermined range and corresponding bits of a respective identifier associated with each of the plurality of elements. The method further comprises presenting each of the plurality of elements to a respective multiplexer. Further the method comprises generating a select signal for an enabled multiplexer in response to finding a match between at least one least significant bit of a respective identifier associated with each of the plurality of elements and a port number of the ordered queue. Finally, the method comprises forwarding a packet associated with a selected element identifier to a matching port number of the ordered queue from the enabled multiplexer.

CROSS REFERENCE TO RELATED APPLICATIONS

The present application is a continuation of U.S. patent applicationSer. No. 14/052,571, filed Oct. 11, 2013, entitled “METHOD AND APPARATUSFOR SORTING ELEMENTS IN HARDWARE STRUCTURES,” naming Mohammad Abdallahas inventor, and having attorney docket number SMII-0193.US, which isherein incorporated by reference in its entirety, and which claims thebenefit of Provisional Patent Application No. 61/793,752, entitled“Method and Apparatus for Sorting Elements in Hardware Structures,”having a filing Date of Mar. 15, 2013, which is herein incorporated byreference in its entirety.

FIELD OF THE INVENTION

Embodiments according to the present invention generally relate tomicroprocessor architecture and more particularly to the architecturefor out-of-order microprocessors.

BACKGROUND OF THE INVENTION

In an Out-Of-Order (“OOO”) microprocessor, instructions are allowed toissue out of their program order. However, in most cases, they arerequired to retire from the machine in order. Further, memory operationsin the machine, regardless of the issue order, need to acquire andupdate memory status in program order. These diverging orderingbehaviors give rise to problems at several locations in amicro-architecture. For example, in most OOO micro-architectures,allocating into queues, e.g., the load-store queue (LSQ), cannot beperformed based on element arrival, which would be more computationallyefficient, because the elements need to be removed in order.

As a result, complexity is often added to the machine, because elementtagging and allocation needs to take place in all resources at the timeof element allocation, e.g., the instruction allocation buffer alsoknown as the “re-order buffer” (“ROB”) needs to perform tagging andallocation of resources at the time of instruction allocation.

For example, FIG. 1 illustrates a pipeline for a conventional OOOmicroprocessor. Instructions are fetched at the fetch stage 102 andplaced in the instruction fetch queue (IFQ) (not shown) within fetchstage 102. The instructions are generally the original assemblyinstructions found in the executable program. These instructionsreference the architectural registers which are stored in register file110. If the first fetched instruction was to be interrupted or raise anexception, the architectural register file 110 stores the results of allinstructions until that point. Stated differently, the architecturalregister file stores the state that needs to be saved and restored inorder to return back to the program during debugging or otherwise.

In an OOO microprocessor, the instructions execute out of order whilestill preserving data dependence constraints. Because instructions mayfinish in an arbitrary order, the architectural register file 110 cannotbe modified by the instructions as they finish because it would make itdifficult to restore their values accurately in the event of anexception or an interrupt. Hence, every instruction that enters thepipeline is provided a temporary register where it can save its result.The temporary registers are eventually written into the architecturalregister file in program order. Thus, even though instructions are beingexecuted out of order, the contents of the architectural register fileschange as though they were being executed in program order.

The ROB 108 facilitates this process. After the instructions aredispatched from the fetch unit 102, they are decoded by decode module104 and are placed in the ROB 108 and issue queue 106 (IQ). The ROB 108and IQ 106 may be part of a scheduler module 172. As instructions areissued out of IQ 106 out of order, they are executed by execute module112.

The write back module 114, in a conventional OOO micro-architecture willwrite the resulting values from those instructions back to the temporaryregisters in ROB 108 first. The ROB 108 keeps track of the program orderin which instructions entered the pipeline and for each of theseinstructions, the ROB maintains temporary register storage. When theoldest instructions in the ROB produce a valid result, thoseinstructions can be safely “committed.” That is, the results of thoseinstructions can be made permanent since there is no earlier instructionthat can raise a mispredict or exception that may undo the effect ofthose instructions. When instructions are ready to be committed, the ROB108 will move the corresponding values in the temporary registers forthose instructions to the architectural register file 110. Therefore,through the ROB's in-order commit process, the results in the registerfile 110 are made permanent and architecturally visible.

By using the ROB 108 module as an intermediary between the write backmodule 114 and the register file 110, a delay at the commit stage isintroduced by conventional OOO processors. Further, in order for the ROB108 module to be able to move the values of the temporary registers tothe register file 110 quickly during the commit cycle, the ROB needs tobe placed in relatively close proximity to the register file 110,thereby, introducing an additional constraint on the design of the OOOarchitecture.

The instructions issued out of order from the IQ 106 may also compriseloads and stores. A load instruction uses registers in the register file110 to compute an effective address and, subsequently, brings the datafrom that address in memory 118 into a register in register file 110.The store similarly uses registers in the register file 110 to computean effective address, then transfers data from a register into thataddress in memory 118. Hence, loads and stores must first wait forregister dependencies to be resolved in order to compute theirrespective effective address. Accordingly, each store instruction isqueued in a load/store queue (LSQ) 116 while it is waiting for aregister value to be produced-when it receives the broadcast regardingits availability, the effective address computation part of the store isissued.

Additionally, store instructions are queued in a LSQ because when storesare issued out of order from the IQ 106, there are memory dependenciesbetween loads and the store instructions that need to be resolved beforethey can access memory 118. For example, a load can access the memoryonly after it is confirmed there are no prior stores that refer to thesame address. It is, once again, the ROB 108 that is used to keep trackof the various dependencies between the stores and the loads.

The scheduler 172 can also comprise an index array 140 that the ROB 108communicates with in order to track the various dependencies. The indexarray 140 is used to store tags that the ROB 108 assigns to all load andstore instructions that are dispatched from IQ 106. These tags are usedto designate slots in the LSQ 116 for the store instructions, so thatthe instructions can be allocated in the LSQ 116 in program order. This,in turn, allows memory 118 to be accessed by the store instructions inprogram order. As a result, in conventional OOO processors, additionalstorage can be required for an index array 140 that stores tags for therespective locations of store instructions in the LSQ. Further,additional communication overhead is required to tag all storeinstructions, to convey the tags along with the store instructions tothe LSQ, and to communicate to the LSQ to add the store instructions tothe locations designated by the respective tags.

BRIEF SUMMARY OF THE INVENTION

Accordingly, a need exists for a method and apparatus for a moreefficient and flexible OOO processor architecture, whereby, elements canbe entered unordered into the various structures, e.g., the LSQ,register file, etc. at allocation time instead of expending the memoryand computational resources up front to order the elements. To avoid thecomplexity of ordering elements at allocation time, this disclosureproposes an efficient and flexible implementation of element orderingfrom an unordered set at retirement time.

In one embodiment, the method and apparatus of the present inventionenable elements in an OOO microprocessor to be ordered at the time ofinstruction retirement as compared to at the time of allocation forconventional OOO micro-architectures. By ordering elements at the timeof instruction retirement, the re-order buffer is prevented fromdedicating computational resources up-front at allocation time forordering the elements. For example, allowing the write-back module towrite values produced from instruction execution directly into theregister file frees the ROB up from acting as an intermediary betweenthe write-back module and the register file during the commit stage asdescribed above. Additionally, it obviates the constraint of placing theROB in close proximity with the register file.

Further, allowing elements to be allocated unordered into the open slotsof the structures, e.g., the LSQ, the register file, etc. also frees upmemory resources in the scheduler and in the pipeline generally. Forexample, the ROB is no longer required to track tags with an index arrayfor entering stores into the LSQ in program order during instructionallocation. Additionally, the ROB does not need to allocate temporaryregister space for committing elements into the register file in order.

In one embodiment, a method for sorting elements in hardware structuresis disclosed. The method comprises selecting a plurality of elements toorder from an unordered input queue (UIQ) within a predetermined rangein response to finding a match between at least one most significant bitof the predetermined range and corresponding bits of a respectiveidentifier associated with each of the plurality of elements. The methodfurther comprises presenting each of the plurality of elements to arespective multiplexer. Further the method comprises generating a selectsignal for an enabled multiplexer in response to finding a match betweenat least one least significant bit of a respective identifier associatedwith each of the plurality of elements and a port number of the orderedqueue. Finally, the method comprises forwarding a packet associated witha selected element identifier to a matching port number of the orderedqueue from the enabled multiplexer.

In another embodiment, a processor unit that is configured to perform amethod for sorting elements in hardware structures is disclosed. Themethod comprises selecting a plurality of elements to order from anunordered input queue (UIQ) within a predetermined range in response tofinding a match between at least one most significant bit of thepredetermined range and corresponding bits of a respective identifierassociated with each of the plurality of elements. The method furthercomprises presenting each of the plurality of elements to a respectivemultiplexer. Further the method comprises generating a select signal foran enabled multiplexer in response to finding a match between at leastone least significant bit of a respective identifier associated witheach of the plurality of elements and a port number of the orderedqueue. Finally, the method comprises forwarding a packet associated witha selected element identifier to a matching port number of the orderedqueue from the enabled multiplexer.

In a different embodiment, an apparatus for sorting elements in hardwarestructures is disclosed. The apparatus comprises a memory, a processorcommunicatively coupled to the memory, wherein the processor isconfigured to process instructions out of order, and further wherein theprocessor is configured to: (a) select a plurality of elements to orderfrom an unordered input queue (UIQ) within a predetermined range inresponse to finding a match between at least one most significant bit ofthe predetermined range and corresponding bits of a respectiveidentifier associated with each of the plurality of elements, whereinthe UIQ comprises a plurality of out of order elements; (b) present eachof the plurality of elements to a respective multiplexer; (c) generate aselect signal for an enabled multiplexer associated with each element inresponse to finding a match between at least one least significant bitof a respective identifier associated with each of the plurality ofelements and a port number of the ordered queue; and (d) forward apacket associated with a selected element identifier to a matching portnumber of the ordered queue from the enabled multiplexer.

The following detailed description together with the accompanyingdrawings will provide a better understanding of the nature andadvantages of the present invention.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the present invention are illustrated by way of example,and not by way of limitation, in the figures of the accompanyingdrawings and in which like reference numerals refer to similar elements.

FIG. 1 is an exemplary diagram of a pipeline for a conventional out oforder microprocessor.

FIG. 2 is an exemplary computer system in accordance with embodiments ofthe present invention.

FIG. 3 is an exemplary diagram of a pipeline for an out of ordermicroprocessor in which elements are ordered at instruction retirementtime in accordance with embodiments of the present invention.

FIG. 4 is a block diagram illustrating an exemplary retirement cycle inwhich elements are selected for retirement from an unordered input queuein accordance with embodiments of the present invention.

FIG. 5 is a block diagram illustrating an exemplary retirement cycle inwhich elements are sorted into an ordered retirement queue in accordancewith embodiments of the present invention.

FIG. 6 depicts a flowchart for an exemplary computer controlled processfor selecting and sorting elements into an ordered retirement queue inan out of order micro-architecture in accordance with embodiments of thepresent invention.

DETAILED DESCRIPTION OF THE INVENTION

Reference will now be made in detail to the various embodiments of thepresent disclosure, examples of which are illustrated in theaccompanying drawings. While described in conjunction with theseembodiments, it will be understood that they are not intended to limitthe disclosure to these embodiments. On the contrary, the disclosure isintended to cover alternatives, modifications and equivalents, which maybe included within the spirit and scope of the disclosure as defined bythe appended claims. Furthermore, in the following detailed descriptionof the present disclosure, numerous specific details are set forth inorder to provide a thorough understanding of the present disclosure.However, it will be understood that the present disclosure may bepracticed without these specific details. In other instances, well-knownmethods, procedures, components, and circuits have not been described indetail so as not to unnecessarily obscure aspects of the presentdisclosure.

Notation and Nomenclature

Some portions of the detailed descriptions that follow are presented interms of procedures, logic blocks, processing, and other symbolicrepresentations of operations on data bits within a computer memory.These descriptions and representations are the means used by thoseskilled in the data processing arts to most effectively convey thesubstance of their work to others skilled in the art. In the presentapplication, a procedure, logic block, process, or the like, isconceived to be a self-consistent sequence of steps or instructionsleading to a desired result. The steps are those utilizing physicalmanipulations of physical quantities. Usually, although not necessarily,these quantities take the form of electrical or magnetic signals capableof being stored, transferred, combined, compared, and otherwisemanipulated in a computer system. It has proven convenient at times,principally for reasons of common usage, to refer to these signals astransactions, bits, values, elements, symbols, characters, samples,pixels, or the like.

It should be borne in mind, however, that all of these and similar termsare to be associated with the appropriate physical quantities and aremerely convenient labels applied to these quantities. Unlessspecifically stated otherwise as apparent from the followingdiscussions, it is appreciated that throughout the present disclosure,discussions utilizing terms such as “entering,” “selecting,” “gating,”“presenting.” “sorting,” “allocating,” “associating,” “determining,”“identifying,” “caching,” “reading,” “writing,” or the like, refer toactions and processes (e.g., flowchart 600 of FIG. 6) of a computersystem or similar electronic computing device or processor (e.g., system210 of FIG. 2). The computer system or similar electronic computingdevice manipulates and transforms data represented as physical(electronic) quantities within the computer system memories, registersor other such information storage, transmission or display devices.

Embodiments described herein may be discussed in the general context ofcomputer-executable instructions residing on some form ofcomputer-readable storage medium, such as program modules, executed byone or more computers or other devices. By way of example, and notlimitation, computer-readable storage media may comprise non-transitorycomputer-readable storage media and communication media; non-transitorycomputer-readable media include all computer-readable media except for atransitory, propagating signal. Generally, program modules includeroutines, programs, objects, components, data structures, etc., thatperform particular tasks or implement particular abstract data types.The functionality of the program modules may be combined or distributedas desired in various embodiments.

Computer storage media includes volatile and nonvolatile, removable andnon-removable media implemented in any method or technology for storageof information such as computer-readable instructions, data structures,program modules or other data. Computer storage media includes, but isnot limited to, random access memory (RAM), read only memory (ROM),electrically erasable programmable ROM (EEPROM), flash memory or othermemory technology, compact disk ROM (CD-ROM), digital versatile disks(DVDs) or other optical storage, magnetic cassettes, magnetic tape,magnetic disk storage or other magnetic storage devices, or any othermedium that can be used to store the desired information and that canaccessed to retrieve that information.

Communication media can embody computer-executable instructions, datastructures, and program modules, and includes any information deliverymedia. By way of example, and not limitation, communication mediaincludes wired media such as a wired network or direct-wired connection,and wireless media such as acoustic, radio frequency (RF), infrared, andother wireless media. Combinations of any of the above can also beincluded within the scope of computer-readable media.

FIG. 2 is a block diagram of an example of a computing system 210capable of being integrated with a processor 214 of an embodiment of thepresent disclosure. Computing system 210 broadly represents any singleor multi-processor computing device or system capable of executingcomputer-readable instructions. Examples of computing system 210include, without limitation, workstations, laptops, client-sideterminals, servers, distributed computing systems, handheld devices, orany other computing system or device. In its most basic configuration,computing system 210 may include at least one processor 214 of anembodiment of the present invention and a system memory 216.

Processor 214 incorporates embodiments of the present invention andgenerally represents any type or form of processing unit capable ofprocessing data or interpreting and executing instructions. In certainembodiments, processor 214 may receive instructions from a softwareapplication or module. These instructions may cause processor 214 toperform the functions of one or more of the example embodimentsdescribed and/or illustrated herein. In one embodiment, processor 214may be an out of order microprocessor. In a different embodiment,processor 214 may be a superscalar processor. In yet another embodiment,processor 214 may comprise multiple processors operating in parallel.

System memory 216 generally represents any type or form of volatile ornon-volatile storage device or medium capable of storing data and/orother computer-readable instructions. Examples of system memory 216include, without limitation, RAM, ROM, flash memory, or any othersuitable memory device. Although not required, in certain embodimentscomputing system 210 may include both a volatile memory unit (such as,for example, system memory 216) and a non-volatile storage device (suchas, for example, primary storage device 232).

Computing system 210 may also include one or more components or elementsin addition to processor 214 and system memory 216. For example, in theembodiment of FIG. 2, computing system 210 includes a memory controller218, an input-output (I/O) controller 220, and a communication interface222, each of which may be interconnected via a communicationinfrastructure 212. Communication infrastructure 212 generallyrepresents any type or form of infrastructure capable of facilitatingcommunication between one or more components of a computing device.Examples of communication infrastructure 212 include, withoutlimitation, a communication bus (such as an Industry StandardArchitecture (ISA), Peripheral Component Interconnect (PCI), PCI Express(PCIe), or similar bus) and a network.

Memory controller 218 generally represents any type or form of devicecapable of handling memory or data or controlling communication betweenone or more components of computing system 210. For example, memorycontroller 218 may control communication between processor 214, systemmemory 216, and I/O controller 220 via communication infrastructure 212.

I/O controller 220 generally represents any type or form of modulecapable of coordinating and/or controlling the input and outputfunctions of a computing device. For example, I/O controller 220 maycontrol or facilitate transfer of data between one or more elements ofcomputing system 210, such as processor 214, system memory 216,communication interface 222, display adapter 226, input interface 230,and storage interface 234.

Communication interface 222 broadly represents any type or form ofcommunication device or adapter capable of facilitating communicationbetween example computing system 210 and one or more additional devices.For example, communication interface 222 may facilitate communicationbetween computing system 210 and a private or public network includingadditional computing systems. Examples of communication interface 222include, without limitation, a wired network interface (such as anetwork interface card), a wireless network interface (such as awireless network interface card), a modem, and any other suitableinterface. In one embodiment, communication interface 222 provides adirect connection to a remote server via a direct link to a network,such as the Internet. Communication interface 222 may also indirectlyprovide such a connection through any other suitable connection.

Communication interface 222 may also represent a host adapter configuredto facilitate communication between computing system 210 and one or moreadditional network or storage devices via an external bus orcommunications channel. Examples of host adapters include, withoutlimitation, Small Computer System Interface (SCSI) host adapters,Universal Serial Bus (USB) host adapters, IEEE (Institute of Electricaland Electronics Engineers) 1394 host adapters, Serial AdvancedTechnology Attachment (SATA) and External SATA (eSATA) host adapters,Advanced Technology Attachment (ATA) and Parallel ATA (PATA) hostadapters, Fibre Channel interface adapters, Ethernet adapters, or thelike. Communication interface 222 may also allow computing system 210 toengage in distributed or remote computing. For example, communicationinterface 222 may receive instructions from a remote device or sendinstructions to a remote device for execution.

As illustrated in FIG. 2, computing system 210 may also include at leastone display device 224 coupled to communication infrastructure 212 via adisplay adapter 226. Display device 224 generally represents any type orform of device capable of visually displaying information forwarded bydisplay adapter 226. Similarly, display adapter 226 generally representsany type or form of device configured to forward graphics, text, andother data for display on display device 224.

As illustrated in FIG. 2, computing system 210 may also include at leastone input device 228 coupled to communication infrastructure 212 via aninput interface 230. Input device 228 generally represents any type orform of input device capable of providing input, either computer- orhuman-generated, to computing system 210. Examples of input device 228include, without limitation, a keyboard, a pointing device, a speechrecognition device, or any other input device.

As illustrated in FIG. 2, computing system 210 may also include aprimary storage device 232 and a backup storage device 233 coupled tocommunication infrastructure 212 via a storage interface 234. Storagedevices 232 and 233 generally represent any type or form of storagedevice or medium capable of storing data and/or other computer-readableinstructions. For example, storage devices 232 and 233 may be a magneticdisk drive (e.g., a so-called hard drive), a floppy disk drive, amagnetic tape drive, an optical disk drive, a flash drive, or the like.Storage interface 234 generally represents any type or form of interfaceor device for transferring data between storage devices 232 and 233 andother components of computing system 210.

In one example, databases 240 may be stored in primary storage device232. Databases 240 may represent portions of a single database orcomputing device or it may represent multiple databases or computingdevices. For example, databases 240 may represent (be stored on) aportion of computing system 210. Alternatively, databases 240 mayrepresent (be stored on) one or more physically separate devices capableof being accessed by a computing device, such as computing system 210.

Continuing with reference to FIG. 2, storage devices 232 and 233 may beconfigured to read from and/or write to a removable storage unitconfigured to store computer software, data, or other computer-readableinformation. Examples of suitable removable storage units include,without limitation, a floppy disk, a magnetic tape, an optical disk, aflash memory device, or the like. Storage devices 232 and 233 may alsoinclude other similar structures or devices for allowing computersoftware, data, or other computer-readable instructions to be loadedinto computing system 210. For example, storage devices 232 and 233 maybe configured to read and write software, data, or othercomputer-readable information. Storage devices 232 and 233 may also be apart of computing system 210 or may be separate devices accessed throughother interface systems.

Many other devices or subsystems may be connected to computing system210. Conversely, all of the components and devices illustrated in FIG. 2need not be present to practice the embodiments described herein. Thedevices and subsystems referenced above may also be interconnected indifferent ways from that shown in FIG. 2. Computing system 210 may alsoemploy any number of software, firmware, and/or hardware configurations.For example, the example embodiments disclosed herein may be encoded asa computer program (also referred to as computer software, softwareapplications, computer-readable instructions, or computer control logic)on a computer-readable medium.

The computer-readable medium containing the computer program may beloaded into computing system 210. All or a portion of the computerprogram stored on the computer-readable medium may then be stored insystem memory 216 and/or various portions of storage devices 232 and233. When executed by processor 214, a computer program loaded intocomputing system 210 may cause processor 214 to perform and/or be ameans for performing the functions of the example embodiments describedand/or illustrated herein. Additionally or alternatively, the exampleembodiments described and/or illustrated herein may be implemented infirmware and/or hardware.

Method and Apparatus for Sorting Elements in Hardware Structures

Embodiments of the present invention provide methods and systems for amore efficient and flexible OOO processor architecture, whereby,elements can be entered unordered into the various structures in aprocessor pipeline, e.g., the LSQ, register file. etc. at allocationtime instead of expending the memory and computational resources upfront to order the elements. To avoid the complexity of orderingelements at allocation time, this disclosure proposes an efficient andflexible implementation of element ordering from an unordered set.

In one embodiment, the method and apparatus of the present inventionenable elements in an OOO microprocessor to be ordered at the time ofinstruction retirement as compared to at the time of allocation forconventional OOO micro-architectures. By ordering elements at the timeof instruction retirement, the re-order buffer is prevented fromdedicating computational resources up-front at allocation time forordering the instruction elements.

For example, allowing the write-back module to write values producedfrom instruction execution directly into the register file frees up theROB from acting as an intermediary between the write-back module and theregister file during the commit stage. Accordingly, the write-backmodule can write the values of executed instructions directly in theregister file. As a result, the present invention obviates theconstraint of placing the ROB in close proximity with the register file.Because the write back module writes directly to the register file, theproximity of the ROB and register file is no longer required to enable arapid transfer of ordered elements from the ROB to the register file.

Further, the ROB is prevented from dedicating resources for tagging andmaintaining an ordering scheme for the stores in the LSQ, which can becomputationally expensive to implement.

Additionally, allowing elements to be allocated unordered into the openslots of the structures, e.g., the LSQ, the register file, etc. alsofrees up memory resources in the scheduler and the pipeline in general.For example, the ROB is no longer required to track tags with an indexarray for entering stores into the LSQ in program order duringinstruction allocation. Additionally, the ROB does not need to allocatetemporary register space for committing elements into the register filein order.

FIG. 3 is an exemplary diagram of a pipeline for an out of ordermicroprocessor in which elements are ordered at instruction retirementtime in accordance with embodiments of the present invention. FIG. 3illustrates that in one embodiment of the present invention, the writeback module 314 advantageously adds unordered elements it receives fromthe execution module 312 directly into the register file 310 instead ofadding them to the ROB 308. In addition FIG. 3 illustrates that, in oneembodiment of the present invention, the ROB 308 controls the orderingof the elements in register file 310 and LSQ 316 at retirement timethrough a retirement interface comprising retirement communicationprotocol 350 as will be explained further below.

As illustrated in FIG. 3, instructions are fetched at the fetch stage302 and placed in the instruction fetch queue (IFQ) (not shown) withinfetch stage 302. These instructions reference the architecturalregisters which are stored in register file 310. After the instructionsare dispatched from the fetch unit 302, they are decoded by decodemodule 304 and are placed in the ROB 308 and issue queue 306 (IQ). Inone embodiment of the present invention, the scheduler module 372comprises the ROB 308 and IQ 306. In a different embodiment, the presentinvention comprises a scheduler module 372 that in itself acts as there-order buffer. As instructions are issued out of IQ 306 out of order,they are executed by execute module 312.

The write back module 314, in one embodiment of the present invention,writes the values resulting from instruction execution directly intoregister file 310 without sorting them. This is advantageous, because noprocessing resources are expended upfront for sorting the elementsbefore they are added to the register file.

Also, it obviates the need for register file 310 to be located in closephysical proximity with the ROB 308 because, as compared with aconventional OOO processor, the ROB 308 does not need to perform a rapidtransfer of ordered elements to the register file 308 during the commitcycle. Instead, the unordered elements are added in physical memory tothe register file 310 in an unordered fashion and are then retired tothe architectural files in order at the retirement stage. Also, bydissociating the register file 310 from the ROB 308, the register file310 is now free to be located in close physical proximity to thegeneration of the register values, e.g., the write back module 314.

Further, when a store is issued out of IQ 306, it can be placed in thefirst available open slot in the LSQ 316 without regard for order. Ascompared with conventional OOO processors, where a store is entered intoa dedicated slot in the LSQ associated with a respective tag assigned bythe ROB 308, the present invention advantageously conserves bothcomputational effort and time at allocation time.

The unordered elements in register file 310 and LSQ 316 are orderedusing a retirement communication protocol 350 at instruction retirementtime. The logic and circuitry for performing the retirement is stored inROB 308. The retirement communication protocol 350 is part of theretirement interface between ROB 308 and both register file 310 and LSQ316. The retirement communication protocol 350 can enable ordering ofthe elements in register file 310 and LSQ 316 before they are retired.The ordered elements in the register file 310 will then preserve andreflect an accurate state of the machine. Further, once the elements inLSQ 316 are ordered, the memory dependencies between them are resolvedand the stores in LSQ 316 can access memory 318 safely. In oneembodiment of the present invention, the retirement communicationprotocol 350 is only used to order elements in either one of theregister file 310 or the LSQ 316 but not both.

FIG. 4 is a block diagram illustrating an exemplary retirement cycle inwhich elements are selected for retirement from an unordered input queuein accordance with embodiments of the present invention. In particular,FIG. 4 illustrates an exemplary retirement cycle wherein unorderedelements within a predetermined retirement range specified by retirementcommunication protocol 350 are selected from unordered input queues sothey can be inserted into an ordered retirement queue. These unorderedinput queues (UIQs) can either be within register file 310 or LSQ 316 orboth. The selection process and retirement range are dictated byretirement communication protocol 350.

The unordered elements placed into register file 310 or LSQ 316 are, inone embodiment, inserted into UIQs 450 maintained within the respectiveregister file 310 or LSQ 316 or both. Each of the elements entered intothe unordered input queue is tagged with an identifier indicating thelocation of the element within the ROB 308. For example, element 451 inUIQ 450 was previously located in position 20 within ROB 308.

The elements in IUQ 450 are moved to an ordered retirement queue (ORQ)480 during the retirement of the associated instructions. As explainedabove, this retirement process, in one embodiment, is used forpotentially moving randomly allocated registers in physical memorywithin register file module 310 to their architectural locations, or tomove stores from an unordered LSQ 316 to the cache memory 318 in order.In other embodiments, the retirement communication protocol 350 can beused to order and retire elements in any other hardware structure in theprocessor as well.

In one embodiment, the retirement communication protocol 350 considersthe tagged identifiers for the elements in the UIQ 450 and confines theretirement procedure to take place in fixed ranges. Accordingly, theprocessor will retire elements in a fixed window before moving on to thenext window of elements. The fixed range, in one embodiment, is variableand can be specific to the design. The retirement communication protocol350 controls the retirement procedure, in one embodiment, bycommunicating the retirement range and the number of elements to beretired to the register file 310 and the LSQ 316.

For example, as ROB 308 commits elements, it can communicate viaretirement communication protocol 350 to the register file 310 or LSQ316 to: (a) a designated retirement range within which to retireelements and (b) the number of elements within that range to retire.

Accordingly, based on the retirement range specified by the retirementcommunication protocol 350, elements are selected from UIQ 450 forordering using the most significant bits of the retirement range. Thenumber of bits which will be required for the selection of the elementsto be ordered will depend on the maximum number of elements that can beretired in a given cycle.

For example, if the size of an element identifier is given by E_(s) andmaximum elements allowed to retire in a cycle (retirement range) isgiven by N, the number of bits required to identify elements for a givenretirement range specified by the retirement communication protocol 350will be determined by the following equation:

S=E_(s)−log₂N, where S signifies the number of most significant bits ofthe retirement range, which will be common across all the identifiersfor the elements within the IUQ 450 for that retirement range. In oneembodiment, the retirement range will be a power of 2 in keeping withthe binary organization of most elements in a microprocessor. As will bediscussed in connection with FIG. 5 below, the remaining bits of theelement identifier E_(s) will form the count which will be used to orderthe elements.

FIG. 4 illustrates an example of how elements can be selected to retirefrom the IUQ 450 and prepared for port assignment in an exemplaryretirement cycle. The size of the element identifier in the example ofFIG. 4 is 5 bits and the maximum retirement range is restricted to be 8elements. The number of bits, S, required to identify and select theproper elements in the retirement range designated by retirementcommunication protocol 350 is therefore 2 (5−log₂8).

The IUQ 450 of FIG. 4 has 14 elements when the Retire Range read enablesignal 411 is asserted. The range to be retired in the cycle illustratedin FIG. 4 is from 16 through 23, which is a range of 8 with thecorresponding binary values shown in FIG. 4 within IUQ 450. Thedesignated range to be retired will be communicated via the retirementcommunication protocol 350. Only the two most significant bits 410(5−log₂8) of the element identifiers are used to perform the contentaddress match (CAM) to read the proper range of elements using the ReadRetire Range interface 460. The remaining three least significant bitsof the element identifier are typically not relevant to the selectionprocess. The 2 most significant bits 410 for all element identifiers inthe range 16 through 23 in IUQ 450 are 2′b10. These 2 CAM mostsignificant bits are used to determine the Retire Range read enablesignal 411 to select the elements in the correct range. Using the RetireRange read enable signal 411, the elements are read out to the inputunit 470 for port mapping and ordering as will be explained inconnection with FIG. 5 below.

However, if for instance, the ROB 308 had committed 10 elements,ranging, for example, from 16 to 25, instead of 8 elements as describedabove, then two retirement cycles would be required to retire all theelements because the maximum retirement range is preset to 8 elements inthe example illustrated in FIG. 4. In such a case the remaining twoelements, 24 and 25, would be retired in a separate retirement cycleduring which the Retire Range read enable signal 411 would need to readout elements that had (2′b11) as their 2 CAM most significant bits.However, only two elements, 24 and 25, would be retired in the secondcycle. By fixing the retirement range to a power of 2, the presentinvention advantageously avoids having to perform an expensive “greaterthan” and “less than” computational operation to select elements withinan arbitrary range that is not a power of 2. Instead, a simpler CAMmatch or XOR operation can be performed in accordance with an embodimentof the present invention to match elements with the retirement rangeselected by retirement communication protocol 250.

FIG. 5 is a block diagram illustrating an exemplary retirement cycle inwhich elements are sorted into an ordered retirement queue in accordancewith embodiments of the present invention. In particular, FIG. 5illustrates how ordering and port mapping takes place in the exemplaryretirement cycle of FIG. 4, once the element selection has completed andthe elements are read out to input unit 470. The retirementcommunication protocol 350 communicated from the ROB 308 will determinethe number of elements that need to be ordered and port mapped. Forexample, if the retirement range in FIG. 4 is 16 to 23, and the ROB 308has committed all 8 elements, then all 8 elements in input unit 470 willget ordered and port mapped.

As shown in FIG. 4, each element in input unit 470 is presented to amultiplexer 475 for each port of the ORQ 480. Each port of ORQ 480 has amultiplexer 475 gating its input. FIG. 5 illustrates the port mappinglogic for Port 1 (3′b001) 580. This logic can be replicated for eachport of the ORQ or any logic that finally holds ordered elements. First,the select signals for the multiplexers 475 are generated. To generatethe encoded select signal (WR_SEL) 520 for the input multiplexer 575,the 3 least significant bits of the element identifiers in the inputunit 470 are compared against the port number of each port using portCAM circuitry 555. If the port CAM circuitry indicates a match with the3 least significant bits of an element identifier, e.g., element 17 inFIG. 5, a 1 hot encoded signal, WR SEL 520, for the input multiplexerfor the port is created.

In the case illustrated in FIG. 5, the port being arbitrated for is Port1 580. The element intended for Port 1 580 is input 550 into multiplexer575, which corresponds with element 17. The 3 least significant bits of17 are 3b′001. Since the select range is 16-23 (5′b10000-5′b11111), andthe least 3 significant bits of 17 (5′b100001) match the port number(3′b001), the packet or value associated with element 17 is selected andmapped on signal WR VALUE 510 and subsequently mapped to Port 1 580. Inone embodiment, the write enable for the respective port, e.g., Port 1,is generated by performing a logical OR of the WR SEL signal 520.

As discussed above, the retirement communication protocol 350 dictateshow many elements in the input unit 470 are to be retired in a givencycle. Accordingly, all elements in input unit 470 that are to beretired within the retirement range 16-23 will also be retired in thesame cycle as element 17 for the example shown in FIGS. 4 and 5. As withelement 17, the 3 least significant bits of the identifiers will be usedto order and port map the elements within the selected range window(16-23). However, it is not necessary for the input unit 470 or ORQ 480to be full when the elements are retired, e.g., less than the full setof 8 elements can also be retired in any particular cycle in the exampleshown in FIGS. 4 and 5. The retirement communication protocol 350 willtypically dictate how many elements are to be retired.

At the end of the retirement process then, the ORQ 480 will have anordered list of elements. In the case of the selecting and sortingcircuitry of the present invention being applied to order stores from anunordered LSQ, the circuitry ensures that the ORQ 480 will retire thestores to memory in program order. The same will apply to the case ofwriting unordered registers in register file 310 back to thearchitectural register file.

FIG. 6 depicts a flowchart for an exemplary computer controlled processfor selecting and sorting elements into an ordered retirement queue inan out of order micro-architecture in accordance with embodiments of thepresent invention. While the various steps in this flowchart arepresented and described sequentially, one of ordinary skill willappreciate that some or all of the steps can be executed in differentorders and some or all of the steps can be executed in parallel.Further, in one or more embodiments of the invention, one or more of thesteps described below can be omitted, repeated, and/or performed in adifferent order. Accordingly, the specific arrangement of steps shown inFIG. 6 should not be construed as limiting the scope of the invention.Rather, it will be apparent to persons skilled in the relevant art(s)from the teachings provided herein that other functional flows arewithin the scope and spirit of the present invention. Flowchart 600 maybe described with continued reference to exemplary embodiments describedabove, though the method is not limited to those embodiments

At step 602, unordered elements are entered into an UIQ 450. Asexplained above, either the register file 310 or LSQ 316 or bothcomprise a respective UIQ for holding unordered elements before they areordered in preparation for retirement.

At step 604, elements from the UIQ 450 are selected for retirement basedon the retirement range specified by retirement communication protocol350 and the associated element identifiers. The retirement range, in oneembodiment, is a power of 2, which allows the most significant bits ofthe elements to be used for selecting the elements by performing a CAMmatch.

The selected elements at step 606 are entered into a temporary buffer,illustrated in FIGS. 4 and 5 as input unit 470 before they are sortedand port mapped into an ordered retirement queue.

At step 608, each element within input unit 470 is presented to amultiplexer 475. Each multiplexer 475 gates the input to each of the ORQ480 ports.

At step 610, the least significant bits of the element identifiers canbe used to generate a WR SEL 520 enable signal to map the element to theappropriate port of ORQ 480 via a WR VALUE 510 signal. The leastsignificant bits of the identifier are matched with the port numbers byusing CAM circuitry 555 and generating the WR SEL 520 enable signal forthe input multiplexer to the port in response to finding a match. Asexplained above, each port of ORQ 480 is gated by a respectivemultiplexer that is enabled by a WR SEL signal and outputs a WR VALUEsignal with the element packet for the respective port.

Finally, at step 612, element packets associated with the selectedelement identifiers can be transferred to the appropriate ports on ORQ480 through the enabled multiplexers. The ORQ 480 now comprises anordered set of elements and can be retired in program order.

While the foregoing disclosure sets forth various embodiments usingspecific block diagrams, flowcharts, and examples, each block diagramcomponent, flowchart step, operation, and/or component described and/orillustrated herein may be implemented, individually and/or collectively,using a wide range of hardware, software, or firmware (or anycombination thereof) configurations. In addition, any disclosure ofcomponents contained within other components should be considered asexamples because many other architectures can be implemented to achievethe same functionality.

The process parameters and sequence of steps described and/orillustrated herein are given by way of example only. For example, whilethe steps illustrated and/or described herein may be shown or discussedin a particular order, these steps do not necessarily need to beperformed in the order illustrated or discussed. The various examplemethods described and/or illustrated herein may also omit one or more ofthe steps described or illustrated herein or include additional steps inaddition to those disclosed.

While various embodiments have been described and/or illustrated hereinin the context of fully functional computing systems, one or more ofthese example embodiments may be distributed as a program product in avariety of forms, regardless of the particular type of computer-readablemedia used to actually carry out the distribution. The embodimentsdisclosed herein may also be implemented using software modules thatperform certain tasks. These software modules may include script, batch,or other executable files that may be stored on a computer-readablestorage medium or in a computing system. These software modules mayconfigure a computing system to perform one or more of the exampleembodiments disclosed herein.

The foregoing description, for purpose of explanation, has beendescribed with reference to specific embodiments. However, theillustrative discussions above are not intended to be exhaustive or tolimit the invention to the precise forms disclosed. Many modificationsand variations are possible in view of the above teachings. Theembodiments were chosen and described in order to best explain theprinciples of the invention and its practical applications, to therebyenable others skilled in the art to best utilize the invention andvarious embodiments with various modifications as may be suited to theparticular use contemplated.

Embodiments according to the invention are thus described. While thepresent disclosure has been described in particular embodiments, itshould be appreciated that the invention should not be construed aslimited by such embodiments, but rather construed according to the belowclaims.

What is claimed is:
 1. A method for sorting elements in an orderedretirement queue, the method comprising: selecting a plurality ofelements to order from an unordered input queue (UIQ) of a register fileof a processor; presenting each element of the plurality of elements toa multiplexer, wherein the multiplexer outputs to a port of the orderedretirement queue; determining a match between a port number of the portand at least one least significant bit of an identifier of an element inthe plurality of elements; and generating a select signal for themultiplexer corresponding to the element in the plurality of elements.2. The method of claim 1, wherein the selecting comprises: selectingelements within a range in response to finding a match between at leastone most significant bit of the range and corresponding bits of arespective identifier operable to tag each of the plurality of elements.3. The method of claim 1, further comprising: forwarding a packetcorresponding to the element of the plurality of elements to the port ofthe ordered retirement queue from the UIQ using the multiplexer.
 4. Themethod of claim 1, further comprising: writing the packet into the portof the ordered retirement queue.
 5. The method of claim 2, wherein theselecting and the generating are performed in response to acommunication protocol controlled by a reorder buffer in a pipeline ofthe processor, and wherein the communication protocol communicates therange and a number of elements to be ordered to the register file. 6.The method of claim 5, wherein the communication protocol indicates anumber of elements to be retired during a clock cycle from the orderedretirement queue.
 7. The method of claim 1, wherein the ordered queuecomprises elements to be retired from the register file in a retirementcycle of a pipeline of the processor.
 8. The method of claim 3, whereinthe determining determines a match using port content address match(CAM) circuitry, wherein the select signal is generated in response tothe CAM circuitry indicating a match.
 9. The method of claim 8, whereina write enable signal is generated for the port by performing a logicalOR of the select signal.
 10. A non-transitory machine-readable mediumthat stores instructions, which when executed by a processor of acomputing device, cause the computing device to: select a plurality ofelements to order from an unordered input queue (UIQ) of a register fileof the processor; present each element of the plurality of elements to amultiplexer, wherein the multiplexer outputs to a port of an orderedretirement queue; determine a match between a port number of the portand at least one least significant bit of an identifier of an element inthe plurality of elements; and generate a select signal for themultiplexer corresponding to the element in the plurality of elements.11. The non-transitory machine-readable medium of claim 10, wherein theselecting comprises: selecting elements within a range in response tofinding a match between at least one most significant bit of the rangeand corresponding bits of a respective identifier operable to tag eachof the plurality of elements.
 12. The non-transitory machine-readablemedium of claim 10, wherein the instructions further cause the computingdevice to: forward a packet corresponding to the element of theplurality of elements to the port of the ordered retirement queue fromthe UIQ using the multiplexer.
 13. The non-transitory machine-readablemedium of claim 10, wherein the instructions further cause the computingdevice to: write the packet into the port of the ordered retirementqueue.
 14. The non-transitory machine-readable medium of claim 11,wherein the selecting and the generating are performed in response to acommunication protocol controlled by a reorder buffer in a pipeline ofthe processor, and wherein the communication protocol communicates therange and a number of elements to be ordered to the register file. 15.The non-transitory machine-readable medium of claim 14, wherein thecommunication protocol indicates a number of elements to be retiredduring a clock cycle from the ordered retirement queue.
 16. Thenon-transitory machine-readable medium of claim 10, wherein the orderedqueue comprises elements to be retired from the register file in aretirement cycle of a pipeline of the processor.
 17. The non-transitorymachine-readable medium of claim 12, wherein the determining determinesa match using port content address match (CAM) circuitry, wherein theselect signal is generated in response to the CAM circuitry indicating amatch.
 18. The non-transitory machine-readable medium of claim 17,wherein a write enable signal is generated for the port by performing alogical OR of the select signal.
 19. An apparatus for sorting elementsstored in hardware structures, said apparatus comprising: a memory; aprocessor communicatively coupled to said memory, wherein said processoris configured to process instructions out of order, and further whereinsaid processor is configured to: select a plurality of elements to orderfrom an unordered input queue (UIQ); present each element of theplurality of elements to a multiplexer, wherein the multiplexer outputsto a port of an ordered retirement queue; determine a match between aport number of the port and at least one least significant bit of anidentifier of an element in the plurality of elements; and generate aselect signal for the multiplexer corresponding to the element in theplurality of elements.
 20. The apparatus of claim 19, wherein saidprocessor is further configured to: forward a packet corresponding tothe element of the plurality of elements to the port of the orderedretirement queue from the UIQ using the multiplexer.